Yangzi Qiao1,2,3, Chao Zou1,2,3, Chuanli Cheng1, Changjun Tie1, Qian Wan1,4, Hao Peng1,5, Dong Liang1, Xin Liu1,2, Hairong Zheng1,2. 1. Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China. 2. Shenzhen Key Laboratory of Ultrasound Imaging and Therapy, Shenzhen, China. 3. These authors contributed equally to this work. 4. Institute of Biomedical and Health Engineering, Shenzhen College of Advanced Technology, University of Chinese Academy of Sciences, Shenzhen, China. 5. Key Laboratory of Imaging Processing and Intelligence Control, School of Artificial Intelligence and Automation, Huazhong University of Science and Technology, Wuhan, China.
Abstract
BACKGROUND: Simultaneous magnetic resonance (MR) acoustic radiation force imaging (ARFI) and MR thermometry (MRT) (STARFI) based on coherent echo-shifted (cES) sequence was proposed and comprehensively compared to radiofrequency (RF)-spoiled gradient echo (spGRE) STARFI. METHODS: Through use of delicately designed gradients, a collection of echoes was delayed by one repetition time (TR) cycle. The crusher gradient after readout (RO) was used as the displacement encoding gradient (DEG). The sequence was intrinsically sensitive to temperature. High-intensity focused ultrasound (HIFU) pulses were interleaved ON/OFF in successive TRs to separate the phase changes induced by displacement due to acoustic radiation force (ARF) impulses and temperature. Bloch simulation was performed to study the phase sensitivity to displacement of the proposed cES STARFI and spGRE STARFI. The proposed cES sequence was evaluated and compared to spGRE STARFI in ex vivo porcine muscle and ex vivo porcine brain. RESULTS: The minimally achievable TR of cES STARFI was shorter than that of spGRE STARFI, indicating that the cES sequence was more time efficient. It was verified through Bloch simulation and ex vivo experiments that the phase sensitivity to displacement of cES STARFI was higher than that of spGRE STARFI. The optimal trigger delays of cES STARFI and spGRE STARFI in ex vivo porcine muscle were toffset =-2 and -1 ms, respectively. The displacement-induced phase change to acoustic pressure slopes of cES STARFI were 0.079, 0.079, and 0.047 rad/Mpa across the three muscle samples, while the slopes of spGRE STARFI were only 0.047, 0.052, and 0.027 rad/Mpa. The maximum temperature difference between cES STARFI and spGRE STARFI was 1.1 °C. In ex vivo porcine brain, both the displacement-induced phase-to-noise ratio (PNRd) and the temperature uncertainty of cES STARFI were better than those of spGRE STARFI (P<0.05). The temperature and displacement-induced phase change maps of cES STARFI and spGRE STARFI during HIFU treatment were in good accordance in time and spatial location. CONCLUSIONS: The cES STARFI sequence can provide simultaneous MR-ARFI and temperature measurements during pulsed HIFU applications. Though the exact displacement cannot be quantified directly, the sequence showed increased phase sensitivity compared with the spGRE sequence and provided efficient visualization of the focal spot. cES STARFI could therefore be a desirable alternative to spGRE STARFI in practical applications. 2020 Quantitative Imaging in Medicine and Surgery. All rights reserved.
BACKGROUND: Simultaneous magnetic resonance (MR) acoustic radiation force imaging (ARFI) and MR thermometry (MRT) (STARFI) based on coherent echo-shifted (cES) sequence was proposed and comprehensively compared to radiofrequency (RF)-spoiled gradient echo (spGRE) STARFI. METHODS: Through use of delicately designed gradients, a collection of echoes was delayed by one repetition time (TR) cycle. The crusher gradient after readout (RO) was used as the displacement encoding gradient (DEG). The sequence was intrinsically sensitive to temperature. High-intensity focused ultrasound (HIFU) pulses were interleaved ON/OFF in successive TRs to separate the phase changes induced by displacement due to acoustic radiation force (ARF) impulses and temperature. Bloch simulation was performed to study the phase sensitivity to displacement of the proposed cES STARFI and spGRE STARFI. The proposed cES sequence was evaluated and compared to spGRE STARFI in ex vivo porcine muscle and ex vivo porcine brain. RESULTS: The minimally achievable TR of cES STARFI was shorter than that of spGRE STARFI, indicating that the cES sequence was more time efficient. It was verified through Bloch simulation and ex vivo experiments that the phase sensitivity to displacement of cES STARFI was higher than that of spGRE STARFI. The optimal trigger delays of cES STARFI and spGRE STARFI in ex vivo porcine muscle were toffset =-2 and -1 ms, respectively. The displacement-induced phase change to acoustic pressure slopes of cES STARFI were 0.079, 0.079, and 0.047 rad/Mpa across the three muscle samples, while the slopes of spGRE STARFI were only 0.047, 0.052, and 0.027 rad/Mpa. The maximum temperature difference between cES STARFI and spGRE STARFI was 1.1 °C. In ex vivo porcine brain, both the displacement-induced phase-to-noise ratio (PNRd) and the temperature uncertainty of cES STARFI were better than those of spGRE STARFI (P<0.05). The temperature and displacement-induced phase change maps of cES STARFI and spGRE STARFI during HIFU treatment were in good accordance in time and spatial location. CONCLUSIONS: The cES STARFI sequence can provide simultaneous MR-ARFI and temperature measurements during pulsed HIFU applications. Though the exact displacement cannot be quantified directly, the sequence showed increased phase sensitivity compared with the spGRE sequence and provided efficient visualization of the focal spot. cES STARFI could therefore be a desirable alternative to spGRE STARFI in practical applications. 2020 Quantitative Imaging in Medicine and Surgery. All rights reserved.
Entities:
Keywords:
High-intensity focused ultrasound (HIFU); acoustic radiation force imaging (ARFI); coherent echo-shifted sequence (cES sequence); magnetic resonance thermometry (MRT)
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